Russian authorities say three people have been detained on suspicion of involvement in the beating of an environmental activist opposed to a controversial highway project near Moscow.

Konstantin Fetisov, a member of the Khimki Forest Defenders movement, has been in a coma since he was attacked last month.

Vladimir Markin, chief spokesman for the Investigative Committee of the Russian Prosecutor-General's Office, told Russian news agencies that the three detained include a Khimki local government official, Andrei Chernyshev.

President Dmitry Medvedev earlier this year suspended construction of the highway through Khimki forest following months of protests, but a government commission this month gave the project the green light.